IMPRESSIVE: Prince William was left in Kate's wake as they hiked to the Tiger's Nest monastery

William struggled to keep up, as it became clear the flushed royal had let his fitness flop while taking a break from official duties.

“So far so good,” William said yesterday, trying not to fall behind. “This view is absolutely stunning.”

The glowing Duchess of Cambridge joked the walk was the perfect way of working off the food she had eaten during the tour.

“It’s a great way to burn off the curry,” she said, as the couple continued their ascent.

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BEAUTIFUL: The Prince admitted the view was stunning

Followed by an entourage of staff, including her hairdresser Amanda Cook Tucker, the mum-of-two chose £475 Penelope Chilvers boots and a £495 Nubuck Shoot waistcoat for the expedition to the ancient monastery, which dates back to 1692.

“It’s a great way to burn off the curry”

Duchess of Cambridge

Three American hikers who bumped into the royals during their trek said the couple looked to be enjoying themselves.

“They were pretty altogether,” said Lauren McKennan, 29, from San Francisco. “There wasn’t a single trail of sweat. They stopped to talk to us for three to five minutes and were absolutely charming.”

When the couple finally made it down the mountain, William admitted the hike had been challenging.

“It was quite tough on the way up,” he said. William’s father, Prince Charles, tried the same climb on a royal visit to the country but never made it to the top.

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ALMOST THERE: The Duke and Duchess of Cambridge spin the prayer wheel at the halfway stage

Charles, who had been injured in a polo match ahead of his trip, stopped on the way to paint a watercolour of the view instead.

When asked about his father’s expedition, William said: “Yes, my father didn’t make it to be top. So that’s something I’ll be reminding him of when I see him.”

William and Kate’s own children Prince George, two, and Princess Charlotte, 11 months, have not accompanied their parents on the visit.

And, after almost a week away from their two tots, the pair said they are missing them “massively”, although they have been in constant contact.

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HAPPY: Fellow hikers said the royals looked to be enjoying themselves

The royals left their children on Sunday as they travelled to India. Asked if they missed their youngsters, William said: “Massively, yes of course.

“And we’re looking forward to seeing them. They’re in good hands.” And asked if he had been able to talk to his son and daughter, he replied: “Yes we have. Many times.”

The couple said they also hope to return to Bhutan with their brood. “It will be lovely if the children could come as well, definitely,” William said.

Kate added: “Maybe when they’re a bit more mobile, I think. “We did actually see one family up there with a small child on their front. It was very brave of them.”

After the trek, the royal couple attended a reception, where Kate looked stunning in a red dress featuring Bhutan’s national flower, the poppy.

The £745 gown is by fashion brand Beulah, which is run by Kate’s pal Lady Natasha Rufus Isaacs.